As business grows more reliant on high-technology, the need for accurate and precise calibration and measurement becomes more imperative than ever. It is desirable to have standards and measurements that are directly traceable to NIST, and to have calibration and test program meet the highest standards of government and industry. Metrology laboratories may also be accredited by such programs as the National Voluntary Laboratory Accreditation Program (NVLAP).
A metrology laboratory might offer acceptance testing, calibration and repairs for instrumentation and standards in a wide array of discipline. Preferably, the metrology laboratory will issue certificates of calibration which can, when required, include as-found/as-left value and measurement uncertainties. A metrology laboratory may be able to calibrate equipment for measurement of temperature, humidity, mass, dimensional, pressure and vacuum, gas flow, force, torque, vibration, electrical, and time/frequency.
A metrology laboratory may also seek to provide complete calibration program management, including recall notification, interval management, reverse trace ability, procedure development, and records management.
A typical process for calibrating a unit under test (“UUT”) for a specific calibration function, is to connect it to a known pre-calibrated source having greater accuracy than the UUT, and then lead a putative measurement on the UUT. At the option of the metrologist, the UUT may then be left as is, merely recording the as-found measurement against the reference output, or optionally adjusted so that the measurement on the UUT matches within appropriate limits the reference. It is possible to independently measure each range of a UUT against a standard, and record the as-found/as-left measurement.
The heart of the metrology laboratory calibration process is the calibration report, generally referred to a data sheet, of a UUT. Typically a data sheet resembles a spreadsheet, with rows containing range data, and columns representing fields. Data sheets may be constructed for specific manufacturer's equipment, for example a Flukes 787 process meter, which contain one row for every function of the UUT to be tested. Functions might include, for example, testing in different voltage ranges corresponding to different dial or switch settings on the UUT. Once a data sheet is determined for that particular make and model, e.g. the appropriate functions are identified and fixed, the data sheet may be saved as a template and can be reused for all UUTs of identical make and model.
In the prior art, a data sheet of calibration data for a particular UUT would typically be saved on an array data structure basis, with one or more identifier such as UUT serial number, ID number, test number, etc., serving as a database index field for the entire test of that UUT. This can be implemented in simple spreadsheet format that can be done by hand, or by using computerized spreadsheet programs such as Microsoft Excel®, or other available programs as will be known to those skilled in the art.
Data saved in an array structure, however, is difficult to maintain, and no easy solution exists for the identification of particular functions (e.g., individual rows in a data sheet) that may need re-calibration or different calibration intervals. Further, no easy solution exists for setting calibration intervals based upon drift analysis rather than failure based tolerance. Also, current data sheet based testing makes it difficult to tie standards to test points and calculate accuracy ratios for individual functions.
What is needed is a way to identify individual functions of a UUT, cross-link standards with these functions, and identify test points that may be problematic. Preferably, such a solution would optionally allow for simultaneous testing of like UUTs, and additionally optionally provide a comprehensive software tool that can augment a current system in place in an existing metrology laboratory, which simplifies and speeds up actual calibration process. Preferably this software tool would optionally perform multiple calibrations, reduce turnaround time, maintain a datasheet library, automate calibrations, calculate tolerances and analyze uncertainties.